CHAMBERS'S INFORMATION FOR THE PEOPLE. 



from all directions to England, to fill up the 

 deficiency, in straight lines. The earth, however, 

 is not at rest, but revolves from west to east ; and 

 as the velocity of rotation diminishes as the lati- 

 tude increases, it is evident that the current which 

 set out, say from Lyon to the north, would, on 

 account of its greater initial velocity when it 

 arrived at Paris, blow no longer directly to the 

 north, but to a point a little to the east of north ; 

 in other words, it would no longer be a south, but 

 a south-west wind. Again, since the current from 

 the north of Scotland had a less velocity than 

 those parts of the earth's surface on which it 

 advanced, it lagged behind, and consequently, 

 by the time it arrived at Silloth in the north 

 of England, had changed from a north to a 

 north-east wind. Similarly, the north-west current 

 changed to a north, the south-west to a west, &c. 

 Hence in a storm the whole system of winds 

 rotates round the centre. It follows in the 

 northern hemisphere that as storms advance, the 

 general veering of the wind at places lying north 

 of the path of their centre is from north-east by 

 north to west ; and at places south of their centre, 

 from north-east by east and south to north-west ; 

 and conversely in the southern hemisphere. 



Next, as to the force of the wind : The rule is 

 simple, and without exception viz., the wind blows 

 from a high to a low barometer, and with a force 

 proportioned to the difference of the barometric 

 pressures. Hence, where the isobarometric lines 

 crowd together, the violence of the storm is most 

 felt, and where they are far asunder, the winds are 

 moderate and light. We have stated that the 

 progressive motion of storms varies from 15 to 40 

 miles per hour, which measures the time taken in 

 passing from one place to another, but this gives 

 no indication of the violence of the storm. This 

 is determined by the rotatory velocity of the wind 

 round the centre of the storm, which in Europe 

 and America frequently amounts to 60 or 70 miles 

 an hour continuously for some time. At Liverpool, 

 on the 3d of December 1863, it blew in inter- 

 mittent gusts with a speed of 93 miles an hour 

 a velocity frequently surpassed by storms within 

 the tropics. 



Of the different theories of storms hitherto pro- 

 posed, we need only refer to the rotatory and the 

 centripetal theories. The rotatory, or, as it is com- 

 monly called, the cyclonic theory, was first pro- 

 posed by Piddington, and has since been elaborated 

 by Redfield, Reid, Dove", and others. By this theory 

 storms are considered as revolving round an axis 

 either upright or inclined to the horizon, while at 

 the same time the body of the storm has a pro- 

 gressive motion over the surface of the globe ; the 

 barometric depression, as caused by the centrifugal 

 force, driving the air from the centre to the circum- 

 ference of the storm. A fatal objection to this 

 theory is, that observation conclusively shews that 

 the wind does not rotate in a circle returning into 

 itself, but constantly tends in a spiral towards the 

 centre. Besides, the centrifugal force engendered 

 by such a motion, even if it were a fact, would not 

 be sufficient to depress the barometer at the centre 

 to the hundredth part of the extent that actually 

 takes place. 



' The spiral rotation,' says Mr Buchan, ' instead 

 of the purely circular rotation, of the winds in 

 storms, completely alters the whole complexion of 

 the question of the theory of storms. For since it 



46 



follows from it that enormous quantities of air are 

 constantly being poured all around into the area 

 of the storm, and since, notwithstanding these 

 accessions tending to increase the pressure, obser- 

 vation shews that the pressure is not thereby 

 increased, but on the contrary sometimes dimin- 

 ished, we are forced to the conclusion, that from 

 a large area within and about the centre of the 

 storm a vast ascending current must arise into 

 the upper regions of the atmosphere; and arriving 

 there must flow away over into neighbouring 

 regions. The physical cause of the ascending 

 currents is to be found in the moist and warm, 

 and therefore light, air which all observation 

 shews to prevail in the front and in the central 

 part of storms. And since most of the rain which 

 accompanies storms falls in those parts of the 

 storm, the barometer will be still further reduced 

 by the removal of the elastic aqueous vapour 

 which is condensed into rain-drops, and by the 

 latent heat set free in the condensation of the 

 vapour.' 



An important point is to be able to tell in what 

 direction the centre of a storm is from the place 

 at which we are, and the rule is easy : ' Standing 

 back to the wind, the centre lies to the left hand of 

 the direction in which the wind is blowing. This 

 holds in all places north of the equator, and it 

 furnishes the rule which must be observed by ships 

 in steering out of the course of the storm. From 

 this relation of the winds to the pressure is also 

 deduced the rule for predicting the direction of the 

 wind at particular sea-ports during storms. Thus, 

 suppose at 9 A.M. it be required to know the 

 direction in which the wind will blow in London 

 at 9 P.M., a storm being observed advancing from 

 Ireland towards the east. Information being had 

 through the telegraph of the course the storm is 

 taking, and an inference being drawn from that 

 observed course that at 9 P.M. its centre will be 

 near Liverpool, then at that hour the gale may be 

 expected at London from S.S.W. 



Typhoons are violent storms that blow on the 

 coasts of Tonquin, China, and Japan. They 

 resemble the storms of Western Europe in their 

 general characteristics, but the main features are 

 more strongly marked. The central depression 

 of the barometer is not unusually as much as 28-3 

 inches, and, on rarer occasions, even 27 inches. 



Whirlwinds and Waterspouts. Whirlwinds 

 differ in many respects from storms or typhoons. 

 They seldom continue longer than a minute at any 

 place, and sometimes only a few seconds ; their 

 breadth varies from a few yards to nearly a quarter 

 of a mile ; during their short continuance, the 

 changes of the wind are sudden and violent ; and 

 the barometer is not observed to fall. They are 

 caused by two air-currents coming in contact and 

 causing an eddy. The direction of the eddy of 

 the whirlwinds, especially when the diameter is 

 very small, differs from the rotation of winds 

 in a storm, in that it may take place either 

 way right to left, or left to right according to 

 the direction of the stronger of the two winds 

 which give rise to the whirlwind. In the sandy 

 deserts of the tropics, these eddies draw up with 

 them large clouds of dust, and the whole is borne 

 forward by the wind that may happen to be blow- 

 ing at the time. 



Waterspouts are whirlwinds occurring on the 

 sea or on lakes. When fully formed, they appear 



